Process of forging magnesium and high percentage magnesium alloys



1936. w. SCHMIDT ET AL v PROCESS OF FORGING MAGNESIUM AND HIGHPERCENTAGE MAGNESIUM ALLOYS Filed July 29, 1931 INVENTORS ATTORNEYSPatented nee. is, 1936 UNITED STATES PATENT; i oF F cE PROCESS OFFORGING AND HIGH PERCENTAGE MAGNESIUM ALLOYS Walter Schmidt and HubertAltwicker, Bitterfeld,

Germany,

ors, by mesne assignments, to

Magnesium Development Corporation, a corporation of Delaware ApplicationJuly 29, 1931 Serial No. 553,822 In Germany August 16, 1930 8 Claims.The present invention relates to a process of forging magnesium and highpercentage magnetained by working magnesium and-magnesium alloys areextensively oriented ,crys tallographi cally. Such forgings thusnecessarily vary in their capacity for resisting stresses, of differing15 direction, particularly as regards the ratio between the yield pointof the forging under elongation and compression respectively. This isprobably attributable to the peculiar conditions v of deformation(translation, or twinning) of the individual hexagonal crystals of themetal. A

capacityfor resisting high stresses in only one direction is undesirablein a forging, since, ordinarily, the finished forging is subjected'tostress components of differing direction. This leads to the problem'ofproducing forgings of magnesium, and magnesium alloys, whose capacityfor resisting tension and compression stresses, as far as practicable,is the same in all directions.

The present invention relates to a process for the production ofmagnesium forgings which 30 have, as closely as possible, the sameresistaiice to tension'and compressionstresses in every direction.According to the present invention theorientation ofthe mechanicalproperties in mag nesium forgings is suppressed to a substantial\ 35extent by forging in such a manner that, during the deformation of theoriginal'ingot, the flnal shape and dimensions of the forgings areapproached by stages, and by interposin'g, between thoseindividualstages which serve to lead to thedesired final shape, stages in whichthe forging is effected by blows in a direction at right angles to thedirection of the blows effecting the main direction of deformation inview of the final v 45 shape. Of course, themain direction ofdeformation must alwaysremain predominant; but the interposed changes.of forging direction at right angles to the main directionpreventexcessive crystallographic orientation, check slip of the crystalsand/or retard twinning. In this way, a gradual approximation of thefinal shape is obtained; When, as is possible, the final shaping .l, i;i eflected by swaging' or die-pressing, it is advisable to select thelowest temperature pos- 53 slble (having in mind the shape of the die)so ,as

to prevent recrystallization of the irregular crystalline structureproduced by the previous opera- 1; ons. a

' As a further advantage of the present invention, the forging processitself is facilitated. Since, in the case of magnesium and its alloys,'the deformation substantially occurs by translation of the basal plane,continued deformation in one and the same direction would in combinationwith the uniform orinetation of. the crystals taking place under suchdeformation, lead, in a relatively short time, to a condition in whichthe arrangement of the individual crystals would hinder any furtherdeformation in the same direction. This unfavourable eifect iscounteracted, in the present invention, by the opposingstages ofdirectional deformation so that the finishing of the forging isfacilitated. It is particularly ad,- visable, in cases where the finalshaping step is performed in a die, to select. as the last deforma- 20tion stage prior to swaging or die-pressing, a stage in which thedireetion of deformation is opposed to thedesired main directon ofdeformation in the die. If, for example, it is desired to form, in

the die, an annular body, the dimensions of which are greater radiallythan axially, it is advisable to so forge the work piece that elongationin the radial direction takes place during die-pressing (the final stageof deformation) By this means the flow of the metal in the radialdirection, when .in the die, is substantially-facilitated.

In order to clearly describe the nature of the present invention,reference is made to the accompanying drawing, which illustratesdiagramtically and by way of example a typical em- 5 t ent of theprocess of the present invention. ferring tofthedrawing Fig. l is a viewin elevation of a blank under deformation and rep resentsthe first stageof the process; Figures 2a and 2b, respectively, illustrate a lateralandh: an axial view of the piece, obtained from that sho, in Figure l,in the second stageof the process.

In Figs. 1, 2c and 2b, the broken lines indicate the shape of the blockwhen the particular stage in question is started, whereas the full linesrepresent the final shape of the block on termination of such stage; andFigure 3 represents a side view of .thefinal shape of the object.-

Referring to Fig. l, a is. the original blank, which is first' forged,by an upsettingoperation (see arrow 1' indicating the direction-ofdeformation), into a body shaped as at b. As will be seen from thedrawing, this upsetting operation serves to compress the original blankor billet so as to produce radial outward flow of the ll directionssubstantially normal to the direction of the applied force f. This bodyb is then turned through and, while being continuously rotated onitsaxis (see Fig. 2b and note the arrow j indicating the direction ofrotation) is deformed in a direction which is trans verse to theoriginal direction of deformation by repeated blows in a direction shownby arrow 1 thus efiecting an elongation of the upset block. Due to thecontinuous rotation of the body b on its axis, the blows applied in thedirection indicated by arrow 1 are effective to apply radial pressure ata plurality of points of the previously deformed billet (body b), and itwill be noted that such radial pressure is applied in a directionwhichis always substantially parallel to the directions of metal flow in theinitial compressing operation shown in Fig. 1. By several repetitions ofthese operations, namely alternate up settingand elongation, theupsetting being always slightly predominant, a body of the form shown inFig. 3 is finally obtained, the mechanical properties of which aresubstantially the same in the direction a, g/ and z. The final shapeisthen imparted to this body by forging in the die. Several examples ofthe application of the process of the present invention will now begiven.

Example 1 For producing a forged crank case for a radial engine, a knownmagnesium alloy containing about 8 percent of aluminium may be employed.In such a piece it is necessary that the capacity for resisting stress,both as regards tension and compression, should be as closely aspossible the same in all directions. A crude ingot, 300 mms. in diameterand 600 mms. high, is cast from this alloy and is then upset, as anupright cylinder, at 280-400 0., in the forging press, until the heighthas been reduced by 30 percent. The ingot is then turned on its axis,through 90 from the original direction, and the deformation iscontinued, by forging transversely to the first direction ofdeformation, the ingot being continuously rotatedon its. original axis,

until the diminution produced in the original height of the cylinder inboth operations is reduced to about 15 percent. The ingot is then againturned through 90, and the forging is continued in the same way, byalternate upsetting and elongation, though, in view of the finalshaping, the upsetting predominates in each case. After the originalheight of the cylinder has been reduced by about 70 per cent in thismanner, the final shapingis effected in the-die at 280 C. The resultattained by this process is that the flnishedpiece exhibits practicallythe same elongation yield point both in the direction of the originalcylinder axis and at right angles thereto, namely about 16-18 kgs. persquare millimeter. Atthe same time the compression yield point is verynear the tensile yield point, having been ascertained to be 14-16 kgs.per square millimeter in both directions.

Example 2 mechanical properties at right angles to its axis, because thetransverse or oscillatory stresses occurring at the hub act in thatdirection. Hence, the highly stressed portion in the vicinity of the hubis formed in stages, by alternate forging in directions differing byright angles, with gradual approximation to the final shape, in the man-'ner described in Example 1. In the case of the blade, too, the forgingis performed by alternate elongation, upsetting and broadening. Thefinal shaping, particularly as regards the pitch of the propeller blade,is effected, in a known manner, by pressure in the die.

We claim: I

-1. A process of forging magnesium and high percentage magnesium alloyswhich comprises the steps of compressing a'billet so as to produceradial outward flow of the metal in all directions substantially normalto the direction of the applied force, and applying radial pressure ata-plurality of points of the deformed billet and substantially parallelto the directions of metal flow in the initial compressing operation soas to compensate for. themajor part of the deformation produced in thefirst step.

2. A process of forging magnesium and high percentage magnesium alloyswhich comprises the steps of compressing a billet so as to produce flowof the metal in a direction to produce the shape desired, and applyingpressure to the deformed billet substantially parallel to the directionof metal flow in the initial compressing operation so as to compensatefor the major part of the deformation produced in the first step. v

3. As a new article of manufacture, a forged blank of metal, in whichmagnesium largely predominates, having the substantially unorientedcrystal grain structure throughout characterizing magnesium which hasbeen compressed to flow the metal radially outward and thereaftersubjected to pressure substantially parallel to the directions of metalflow in the initial compressing operation, said blank by virtue of theunorienated crystal structure being further characterized by aresistance to mechanical stresses substantially equal in all directions.I

4. As a new article of manufacture, a forged blank of metal, in whichmagnesium largely predominates and containing about 8 per cent ofaluminum, said blank, having the substantially unoriented crystal grainstructure throughout characterizing magnesium which has been compressedto flow the metal radially outward and thereafter subjected topressuresubstantially parallel to the directions of metal flow-in theinitial compressingoperation, said blank by virtue of the unorientedcrystal structure being further characterized by a resistance tomechanical stresses substantially equal in all directions.

5. A process of forging magnesium and high percentage magnesium alloysin stages which comprises subjecting a billet to forging stages in whichthe billet is compressed so as to produce flow of the metal atsubstantially right angles to the compressive forces, and in a directionto produce the shape desired, and interposing between said forgingstages intermediate forging stages in which pressure is applied to thedeformed billet substantially parallel to the direction of metal flowinthe first-named forging stages, the deformation produced by said intermediate forging stages compensating for the major part of thedeformation produced in the said first-named forging stages am s 1flJiprocessofforgingmagnesiumandhlah percentage magnesium alloys instages which comprises subieoting a billet to forging stages inwhiohthebilletiscompressedsoastoproduce flow of the metal atsubstantially risht angles to the compressive forces, and in a directionto'produce the shape desired, and interposing' between i said forgingstages intermediate forging stages in which pressure is applied to thedeformedbillet substantially parallel to the direction of metal flow inthe first-named forging stages, the

deformation produced. by said intermediate-forgingstagesc'ompensating'for the major part of the deformation produced in the saidfirstnamed' forging stages; the final stage of deformation, beingeffected at the lowest temperature compatible with lastic deformation.

7. A process 0 forging magnesium. and high percentage magnesium alloysin stages which comprises subjectlng'a billet to. forging stages inwhich the billet is compressed so as'to produceflowvof the metal atsubstantially right angles to the compressive forces, and in a directionto rection of flow intheiirst-named forging stagu; the defamationproduced by said intermediate forging stages for the maior partof thedeformation produced in the said nrst-namedforging stages, theiinalstage of deformation being eflected bum.

8..Aprocessofforging in which the billetis "W v duce flow of the metal'ateubstantially right angles to the compressive forces; andin a'direc-' tion to produce de'slredrand ms between said main: stagesintermediate "forgingstages in which pressure isapplied to the vdeformed billet substantially parallel tov the direction of metal flowin the first-named forging- J mumm alloys in. stag which 's'ubiectings"; billet w for! M '10 data pimstages,- the deformation producedby'said-intermediate i-forgi'ng stages for the maior part of thedeformation produced in the.

sald'flrst-named forging stages. the final-stage of deformation beingelected by swaglng at the ormation.

lowest temperature compatible with plastic 4 1- iii l

